UNIT 4 - researching chem - errors , uncertainty , sig figs

Question 1

Accurate

Answer 1

A measurement that is in good agreement with the actual value

Question 2

Precise

Answer 2

Measurements that are in close agreement with each other

Question 3

Reproducible

Answer 3

If the same procedure was carried out by a number of different people and the results are still close together , the results are said to be reproducible

Question 4

The types of error

Answer 4

• Systematic error

- random error

Question 5

Systematic error

Answer 5

Causes results to all be higher or lower than expected. Can be taken into account in calculations (can be corrected). Caused by: faulty equipment, impure Regent, incorrect concentration of solutions.

Question 6

Random error

Answer 6

Occur in all experiments. (Despite how careful you are). Can be reduced by repeating experiments and taking averages of many values. Small random errors occur more than large random errors

Question 7

What is measurement uncertainty

Answer 7

All measurement have a degree of error associated with them.

• measurements can only be carried out to a limited degree of accuracy (depending on equipment used)
• this uncertainty gives a range if values within where the actual value lies

Question 8

Equation for calculating percentage uncertainty

Answer 8

Percentage uncertainty = (uncertainty / quantity measured) x 100

Question 9

Absolute uncertainty equation

Answer 9

Absolute uncertainty = % uncertainty / 100 x measurement

Question 10

Significant figures

: non _____ numbers are always significant

Answer 10

Non zero numbers are always significant eg 1.234 has 4 significant figures and 1.2 has 2 sig figs

Question 11

Zeros between ____ _____ numbers are always significant

Answer 11

Zeros between non zero numbers are always significant eg 6007kg has 4 significant figures and 5.08cm has 3 significant figures

Question 12

Zeros to the ____ of the first non zero number are NOT significant

Answer 12

Zeros to the left of the first non zero number are NOT significant eg 0.0005 has 1 sig fig and 0.321 has 3 sig figs

Question 13

Zeros at the end of numbers are significant IF the number contains a ______ ______

Answer 13

Zeros at the end if numbers are significant if the number contains a decimal point eg 210.0mm has 4 sig figs and 0.0600mol has 3 sig figs

Question 14

Zeros at the end of numbers may or may not be significant if the number contains a ________ _____

Answer 14

Zeros at the end of numbers may or may not be significant if the number contains no decimal point

Question 15

How can the most significant errors be identified

Answer 15

The most significant errors can be identified by comparing individual % errors

Question 16

Explain final / overall percentage error

Answer 16

• when multiplying or dividing quantities subject to errors the overall error in the final quantity needs to be determined.
• all individual errors can be added up and the overall percentage error can be determined ( look at notes for example)

Question 17

Processed results : multiplication and division

Answer 17

Answers given to the same number of significant figures as number with fewest sig figs

Question 18

Processed results : addition or subtraction

Answer 18

Answers are given to same DP as number with fewest DP

Question 19

rounding : what to do with numbers ending in 5

Answer 19

Numbers ending in 5 ; 1.5 , 4.35 etc should be rounded to the even number(p ( 50% it will go up 50% it will go down

Question 20

If in doubt how do you round ?

Answer 20

If ever in doubt , round to 3 significant figures !